"Why is Tim Cook coming out a news story in 2014?" you might ask. "Why can't (as legions of online critics have doubtless asked) gay people 'just get on with their jobs and stop banging on about their sexuality'."

The answer's simple. Because people perform better when they can be themselves at work. It's a simple fact that if you don't have to conceal your sexual orientation from those around you, you'll do better at your job. As any manager knows – and employers know to their cost – preventing staff from achieving their full potential has a massive impact on both their personal performance and on organisational effectiveness.

Being yourself at work is something Stonewall passionately believes in. So do hundreds of major employers in Britain, who are members of our Diversity Champions programme which helps them to create workplaces where their lesbian, gay and bisexual staff will flourish. Collectively they employ a fifth of the UK workforce and it's the largest non-governmental intervention of its kind in the world. Employers including EY, Accenture, Home Office and even MI5 are all members of the programme. They know that the impact of failing to have an inclusive environment is well documented.

Video: Apple CEO Tim Cook speaks out on being gay IBTimes UK

For example, EY conducted global research of its offices which shows that staff working in fully inclusive environments bring in $125,000 per year per head more for the organisation than employees working in parts of the business where they feel they can't be themselves at work.

So, if a staff member isn't able to be themselves at work, their performance suffers. They won't build relationships with their colleagues, evading questions that may 'out' them. Some play the pronoun game. They'll switch the gender of their partner to something that they think will be more palatable to their colleagues. At team building events their partner will always be absent, because 'something came up'. So, while your sexual orientation doesn't define you, it is relevant at work.

For people building their careers Tim Cook coming out also shows that in 2014 your sexual orientation isn't a barrier to success. Time and again young gay people tell us that when they're selecting potential employers they look to see whether any of their senior management talk publicly about their sexual orientation, or whether the organisation talks positively about valuing their gay staff. So when Tim says, 'the company I am so fortunate to lead has long advocated for human rights and equality for all,' this isn't corporate jargon – potential gay staff will hear it as a powerful recruitment pitch.

In modern 21<sup>st century Britain successful lesbian, gay and bisexual business leaders are increasingly visible. They inspire confidence in their junior staff who are concerned about coming out. They can set the corporate tone in their organisations and show that diversity really does lead to a more effective workforce. But there's still much work to do. For all the progress we've made in our councils, law firms and security forces, it's notable that Britain's national game currently has no openly gay male professional footballers,.

Barely 10 years have passed in Britain since the law changed to protect gay staff from discrimination on the grounds of their sexual orientation – and in many American states these protections still don't exist. Anyone whose career started in Britain before 2003 will remember seeing people lose their jobs because of their sexual orientation. It's no surprise that even in this country some who built their careers in these years are cautious about coming out. So for them Tim Cool's coming out may be the most powerful, showing that we're all finally starting to get more comfortable about 'the gay thing' at work.'

James Lawrence is the Communications Officer for Stonewall, one of the world's most visible and courageous LGBT activist groups. You can follow him on Twitter @JamieJ73 or find out more about Stonewall by visiting its website or Twitter feed.